Proximity Effects in electron beam lithography impact feature dimensions, pattern fidelity and uniformity. These effects
are addressed using a mathematical model representing the radial exposure intensity distribution induced by a point
electron source, commonly named as the Point Spread Function (PSF). PSF models are usually employed for predicting
and compensating for effects up to 15μm. It is well known that there are also some process related phenomena that
impact pattern uniformity that have a longer range, namely CMP effects, fogging, etc.
Performing proximity effects corrections can result in lengthy run times as file size and pattern densities continue to
increase exponentially per technology node. Running corrections for extreme long range phenomena becomes
computational and file size prohibitive. Nevertheless, since extreme long range may reach up several millimeters, and
new technology nodes require a high level of precision, a strategy for predicting and compensating these phenomena is
crucial.
In this paper a set of test patterns are presented in order to verify and calibrate the so called extreme long range effects in
the electron beam lithography. Moreover, a strategy to compensate for extreme long range effects based on the pattern
density is presented. Since the evaluation is based on a density map instead of the actual patterns, the computational
effort is feasible.
The proposed method may be performed off-line (in contrast to machine standard in-line correction). The advantage of
employing off-line compensation relies on enhancing the employ of dose and/or geometry modulation. This strategy also
has the advantage of being completely decoupled from other e-beam writer’s internal corrections (like Fogging Effect
Correction - FEC).